1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a liquid crystal display device implementing improved configuration of electrical lines and a fabricating method thereof.
2. Description of Related Art
A typical liquid crystal display device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite orientational order in arrangement resulting from their thin and long shapes. The arrangement direction of the liquid crystal molecules can be controlled by supplying an electric field to the liquid crystal molecules. In other words, as the arrangement direction of the liquid crystal molecules is changed, the arrangement of the liquid crystal molecules also changes. Since Incident light is refracted to the arrangement direction of the liquid crystal molecules due to the optical anisotropy of the arranged liquid crystal molecules image data can be displayed.
By now, an active matrix LCD that the thin film transistors and the pixel electrodes are arranged in the form of a matrix is most attention-getting due to its high resolution and superiority in displaying moving video data.
FIG. 1 shows the configuration of a typical TFT-LCD device. The TFT-LCD device 1 includes upper and lower substrates 10 and 20 with a liquid crystal 50 interposed therebetween. The upper and lower substrates 10 and 20 are called a color filter substrate and an array substrate, respectively.
In the upper substrate 10, on a surface opposing the lower substrate 20, black matrix 12 and color filter layer 14 that includes a plurality of red (R), green (G), and blue (B) color filters are formed in shape of an array matrix such that each color filter is surrounded by the black matrix 12. Further on the upper substrate 10, a common electrode 16 is formed and covers the color filter layer 14 and the black matrix 12.
In the lower substrate 20, on a surface opposing the upper substrate 10, a TFT “T”, as a switching device, is formed in shape of an array matrix corresponding to the color filter layer 14, and a plurality of crossing gate and data lines 26 and 28 are positioned such that each TFT is located near each cross point of the gate and data lines 26 and 28. Further in the lower substrate 20, a plurality of pixel electrodes 22 are formed on an area defined by the gate and data lines 26 and 28. The area there defined is called a pixel portion “P”. The pixel electrode 22 is a transparent conductive metal such as indium tin oxide (ITO).
The above-mentioned upper and lower substrate 10 and 20 are attached to each other using a sealant, and thereafter, the liquid crystal 50 is injected between the upper and lower substrates 10 and 20.
When the TFT “T” is the thin film transistor, which includes source, drain and gate electrodes (not shown), the gate line 26 transmits scanning signals to the gate electrode while the data line 28 transmits video signals to the source electrode. The video signals change alignments of the liquid crystal molecules according to the scanning signals such that the LCD device displays various gray levels.
In a conventional fabricating process for the LCD panel, at least two LCD panels are fabricated employing a large-sized upper substrate as the upper substrate 10. Thereafter, the large sized upper substrate is scribed and broken into at least two upper substrates 10 of FIG. 1 such that at least two independent LCD panels shown in FIG. 1 are produced. The above-mentioned process is called a scribing and breaking process.
The typical LCD device has a drive IC (Integrated Circuit) on its lower substrate. The drive IC serves to apply electric signals to each electric line formed on the lower substrate. To install the drive IC on the lower substrate, various methods, for example, such as chip on board (COB), chip on glass (COG), and tape carrier package (TCP) methods are adopted.
The COB method is conventionally adopted for a segment type LCD device, or a LCD panel having a low resolution. Since the segment type LCD device or the low resolution LCD panel uses a small number of leads, the drive IC thereof has also a small number of leads. Therefor, the driver IC thereof is first installed on a printed circuit board (PCB) having a plurality of leads, and the leads of the PCB are connected with the LCD panel via a proper method, which is relatively simple.
However, as the LCD devices become to have a high resolution, a great number of leads are adopted for the drive IC. When the drive IC has a great number of leads, it is difficult to install the drive IC on the above-mentioned PCB.
In another method, the COG method, the drive IC is directly installed on the LCD panel without interposing the PCB. Therefore, the connection between the drive IC and the LCD panel is stable, and a minute pitch is applicable for the installation of the drive IC. The COG method employs a multi-layered flexible printed circuit (FPC) instead of the PCB. The multi layered FPC contacts the LCD panel via an anisotropic conductive film (ACF) and transmits input signals to the drive IC.
The above-mentioned COG method has advantages of low cost and high stability. However, since a pad of the LCD panel needs an additional area to install the drive IC, the LCD panel should be enlarged. In addition, when the COG method is adopted for the LCD panel, it is difficult to repair against troubles of the drive IC or terminal lines of the LCD panel.
In another method, the TCP method, the drive IC is installed on a polymer film. The TCP method is widely used for the LCD device as well as a mobile phone that need small, thin, and light electrical packages.
FIG. 2 shows a conventional LCD device adopting the COG method.
As shown, a data drive circuit 27 and a gate drive circuit 29 are formed around the lower substrate 20 of the LCD panel 1. The gate drive circuit 29 is electrically connected with the gate lines 26 of FIG. 1, while the data drive circuit 27 is electrically connected with the data lines 28 of FIG. 1. In another aspect, the data and gate drive circuits 27 and 29 are electrically connected with source PCB 33 and gate PCB 31, respectively. The data and gate drive circuits 27 and 29 respectively apply the video and scanning signals from the source and gate PCBs 33 and 31 to the data and gate lines 28 and 26 of FIG. 1.
Still in FIG. 2, the data and gate drive circuits 27 and 29 are directly installed on the lower substrate 20, and a plurality of FPCs 35 are used to connect the drive circuits 27 and 29 with the PCBs 33 and 31. At this point, the FPCs 35 serves as input terminals for transmitting the input signals from the PCBs to the drive circuits. In a reel chip on glass method, one edges of the PCBs 31 and 33 overlap opposing edges of the lower substrate 20, and input terminals are directly formed on the lower substrate 20 to connect the PCBs and the drive circuits.
Further, the data drive circuit 27 receives the video signals directly from the source PCB 33, while the gate drive circuit 29 receives the scanning signals from the source PCB 33 via the gate PCB 31. At this point, to transmit scanning signals from the source PCB 33 to the gate PCB 31, a transmitting FPC 37 is used. The transmitting FPC 37 transmits the gate signals including Vcom, Vgh, Vgl, Vcc, Gsp, Gsc, Coe, and Gnd to the gate PCB 31.
As explained above, since the COG method adopts an additional element, the transmitting FPC, a material cost of the LCD device increases. Further, soldering errors additionally occur in connecting the transmitting FPC 37 with the gate and source FPCs 31 and 33.
FIGS. 3 and 4 illustrate a conventional TCP method. As shown, a source TCP 36 and a gate TCP 34 are used to respectively connect the source and gate PCB 33 and 31 with the data and gate lines 28 and 26. The source and gate TCP 36 and 34 respectively have the data and gate drive circuits (data and gate drive ICs) in themselves as shown in FIG. 4. As shown in FIG. 4, the data or gate drive IC 17 is installed on a polymer film 19, and the polymer film 19 is connected with the lower substrate 20 and the gate or source PCB 31 or 33 via an anisotropic conductive films 18.
Returning to FIG. 3, similarly to the COG method of FIG. 2, the transmitting FPC 37 is used to transmit scanning signals from the source PCB 33 to the gate PCB 31. That is to say, the TCP method also has the same problem as what is mentioned in the explanation of the COG method.